The present invention relates to an automatic brake booster which is used in a brake of an automobile or the like, and more particularly, to an improvement of the valve mechanism thereof.
An automatic brake booster is known in the art which comprises a valve body slidably disposed within a shell, a power piston mounted on the valve body to partition the interior of the shell into a constant pressure chamber and a variable pressure chamber, a valve mechanism for supplying a fluid to or displacing it from the variable pressure chamber, an input shaft for switching the valve mechanism, and a solenoid which drives a solenoid plunger slidably mounted on the valve body back and forth to switch the valve mechanism, the valve mechanism including a first vacuum valve seat formed on the valve body, an atmosphere valve seat formed on the valve plunger which is coupled to the input shaft, and a valve element which becomes seated on the first vacuum valve seat and the atmosphere valve seat from the rear side, the valve element becoming seated upon the first vacuum valve seat and being removed from the atmosphere valve seat as the valve plunger is driven forward and becoming seated upon the atmosphere valve seat and being removed from the first vacuum valve seat as the valve plunger is driven backward.
In an automatic brake booster of the kind described, an output from the power piston is transmitted through an output shaft to an piston of a master cylinder in order to generate a master cylinder liquid pressure. Part of the output is transmitted as a reaction to the valve plunger or the solenoid plunger through a reaction disc. When the input shaft is operated, the valve mechanism is operated in a manner such that the reaction from the reaction disc is balanced with the input from the input shaft. Alternatively, when the solenoid is energized, the valve mechanism is operated such that the excitation by the energized solenoid is balanced with the reaction from the reaction disc. In this manner, a brake output is delivered in accordance with an input from the input shaft or an excitation of the energized solenoid.
However, when an arrangement is employed in which a brake reaction is transmitted to the solenoid plunger, as a brake output is delivered by energizing the solenoid, a transmission path becomes complicated for the solenoid plunger to be operated once and the reaction therefrom be transmitted to the solenoid plunger, resulting in a large variation in the magnitude of reaction which is transmitted to the solenoid plunger and leading to instability of the reaction. In addition, a time lag occurs for the transmission of the reaction to the solenoid plunger. This makes it difficult to achieve a precise control by controlling the current or voltage applied to the solenoid in order to control the brake output.
In view of the foregoing, it is an object of the invention to provide an automatic brake booster which is capable of controlling a brake output when operating as an automatic brake with a high accuracy as compared with a conventional automatic brake booster.
Specifically, in an automatic brake booster including a valve body slidably disposed in a shell, a power piston mounted on the valve body and partitioning the interior of the shell into a constant pressure chamber and a variable pressure chamber, a valve mechanism mounted in the valve body for supplying a fluid to or discharging it from the variable pressure chamber, an input shaft for operating the valve mechanism, and a solenoid for driving a solenoid plunger which is slidably mounted on the valve body back and forth to operate the valve mechanism, the valve mechanism including a first vacuum valve seat formed on the valve body, an atmosphere valve seat formed on a valve plunger which is coupled to the input shaft, and a valve element which can be seated upon the first vacuum valve seat and the atmosphere valve seat, in accordance with the present invention, there is provided a second vacuum valve seat member slidably mounted on the valve body and having a second vacuum valve seat which is juxtaposed with the first vacuum valve seat and on which the valve element can be seated and a pressure responsive area which is subject to a pressure in the variable pressure chamber and a pressure in the constant pressure chamber, the arrangement being such that when the solenoid is energized, the solenoid plunger urges the second vacuum valve seat member against the valve element to switch the valve mechanism so that the acting force which results from a pressure differential between the pressure in the variable pressure chamber and the pressure in the constant pressure chamber and acting upon the pressure responsive area of the second vacuum valve seat member is balanced with the force with which the solenoid plunger is urged, thereby allowing a brake output which depends on the force with which the solenoid plunger is urged to be delivered.
Also, in an automatic brake booster including a valve body slidably disposed in a shell, a power piston mounted on the valve body and partitioning the interior of the shell into a constant pressure chamber and a variable pressure chamber, a valve mechanism mounted in the valve body for supplying a fluid to or discharging it from the variable pressure chamber, an input shaft for operating the valve mechanism, and a solenoid for driving a solenoid plunger which is slidably mounted on the valve body back and forth to operate the valve mechanism, the valve mechanism including a vacuum valve seat formed on the valve body, an atmosphere valve seat formed on a valve plunger which is coupled to the input shaft, and a valve element which can be seated upon the vacuum valve seat and the atmosphere valve seat, in accordance with a second aspect of the invention, there is provided a tubular member slidably mounted on the valve body and having the vacuum valve seat formed thereon and having a pressure responsive area which is subject to a pressure in the variable pressure chamber and to a pressure in the constant pressure chamber, the arrangement being such that upon energization of the solenoid, the solenoid plunger urges the tubular member toward the valve element to switch the valve mechanism and the force with which the solenoid plunger urges the tubular member is balanced with a force acting on the pressure responsive area of the tubular member which results from a pressure differential between the variable pressure chamber and the constant pressure chamber, thereby delivering a brake output which depends on the urging force from the solenoid plunger.
With the arrangement of the invention as mentioned above, when the solenoid is energized to deliver a brake output, the acting force which results from the pressure differential between the pressure in the constant pressure chamber and the pressure in the variable pressure chamber acts as a reaction on the solenoid plunger, whereby the transmission path from the energization of the solenoid to the transmission of the reaction to the solenoid plunger is simplified, minimizing a variation in the reaction and avoiding a time lag in the transmission of the reaction. Consequently, a brake output when operating as an automatic brake can be controlled with a better accuracy as compared with a conventional automatic brake booster.
Above and other objects, features and advantages of the invention will become apparent from the following description of several embodiments thereof with reference to the attached drawings.